Duncan posted on Wed, 18 Jul 2018 07:20:09 +0000 as excerpted: >> As implemented in BTRFS, raid1 doesn't have striping. > > The argument is that because there's only two copies, on multi-device > btrfs raid1 with 4+ devices of equal size so chunk allocations tend to > alternate device pairs, it's effectively striped at the macro level, > with the 1 GiB device-level chunks effectively being huge individual > device strips of 1 GiB. > > At 1 GiB strip size it doesn't have the typical performance advantage of > striping, but conceptually, it's equivalent to raid10 with huge 1 GiB > strips/chunks.
I forgot this bit... Similarly, multi-device single is regarded by some to be conceptually equivalent to raid0 with really huge GiB strips/chunks. (As you may note, "the argument is" and "regarded by some" are distancing phrases. I've seen the argument made on-list, but while I understand the argument and agree with it to some extent, I'm still a bit uncomfortable with it and don't normally make it myself, this thread being a noted exception tho originally I simply repeated what someone else already said in-thread, because I too agree it's stretching things a bit. But it does appear to be a useful conceptual equivalency for some, and I do see the similarity. Perhaps it's a case of coder's view (no code doing it that way, it's just a coincidental oddity conditional on equal sizes), vs. sysadmin's view (code or not, accidental or not, it's a reasonably accurate high-level description of how it ends up working most of the time with equivalent sized devices).) -- Duncan - List replies preferred. No HTML msgs. "Every nonfree program has a lord, a master -- and if you use the program, he is your master." Richard Stallman -- To unsubscribe from this list: send the line "unsubscribe linux-btrfs" in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html
